Z51F3220FNX Datasheet, PDF (108/312 Pages) Zilog, Inc. – Z8051 Series 8-Bit Microcontrollers

Z51F3220
Product Specification
11.3 Watch Dog Timer
11.3.1 Overview
The watchdog timer rapidly detects the CPU malfunction such as endless looping caused by noise or something
like that, and resumes the CPU to the normal state. The watchdog timer signal for malfunction detection can be
used as either a CPU reset or an interrupt request. When the watchdog timer is not being used for malfunction
detection, it can be used as a timer to generate an interrupt at fixed intervals. It is possible to use free running 8-
bit timer mode (WDTRSON=’0’) or watch dog timer mode (WDTRSON=’1’) as setting WDTCR[6] bit. If WDTCR[5]
is written to ‘1’, WDT counter value is cleared and counts up. After 1 machine cycle, this bit is cleared to ‘0’
automatically. The watchdog timer consists of 8-bit binary counter and the watchdog timer data register. When
the value of 8-bit binary counter is equal to the 8 bits of WDTCNT, the interrupt request flag is generated. This
can be used as Watchdog timer interrupt or reset of CPU in accordance with the bit WDTRSON.
The input clock source of watch dog timer is the BIT overflow. The interval of watchdog timer interrupt is decided
by BIT overflow period and WDTDR set value. The equation can be described as
WDT Interrupt Interval = (BIT Interrupt Interval) X (WDTDR Value+1)
11.3.2 WDT Interrupt Timing Waveform
Source Clock
BIT Overflow
WDTCNT[7:0]
0
WDTDR[7:0]
WDTIFR
Interrupt
1
2 30
1
2
3
0
1
2
Counter Clear
n
3
WDTCL
Occur
WDTDR  0000_0011b
Match
Detect
WDTRESETB
RESET
Figure 11.3 Watch Dog Timer Interrupt Timing Waveform
PS029902-0212
PRELIMINARY
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